Abstract:

A turbine blade of the invention includes an air foil including a
plurality of cooling flow passages through which a cooling medium flows
from a leading edge region to a trailing edge region, a top plate which
forms the apex of the air foil, has a heat-resistant coating applied on
the upper surface thereof, and includes a plurality of cooling holes, and
a squealer which protrudes radially outward from the blade from the top
plate, and is formed so as to extend from a leading edge end to a
starting end of the trailing edge region along a suction-surface-side
blade wall in a peripheral direction of the blade.

Claims:

1. A turbine blade comprising:an air foil including a plurality of cooling
flow passages through which a cooling medium flows from a leading edge
region to a trailing edge region;a top plate which forms the apex of the
air foil, has a heat-resistant coating applied on the upper surface
thereof, and includes a plurality of cooling holes; anda squealer which
protrudes radially outward from the blade from the top plate, and is
formed so as to extend from a leading edge end to a starting end of the
trailing edge region along a suction-surface-side blade wall in a
peripheral direction of the blade.

2. A turbine blade comprising:an air foil including a plurality of cooling
flow passages through which a cooling medium flows from a leading edge
region to a trailing edge region;a top plate which forms the apex of the
air foil, has a heat-resistant coating applied on the upper surface
thereof, and includes a plurality of cooling holes; anda squealer which
protrudes radially outward of the blade from the top plate, is formed
from a starting end of the trailing edge region along a
suction-surface-side blade wall to a leading edge end in a peripheral
direction of the blade, and is further formed so as to continuously
extend from the leading edge end along a pressurized-surface-side blade
wall to the starting end of the trailing edge region.

3. The turbine blade according to claim 1, whereinthe height of the top
plate is set to be lower than the height of the top surface of the
squealer by at least a predetermined value in consideration of variations
in the finished height of the heat-resistant coating.

4. The turbine blade according to claim 1, whereinthe height of the top
plate of the leading edge region is formed so as to be lower than the
height of the top plate of the trailing edge region, and an inclined
portion which has an upward gradient toward the trailing edge region from
the leading edge region is formed.

5. The turbine blade according to claim 1, whereinthe plurality of cooling
holes is arranged in a double line on the top surface of the squealer or
the upper surface of the top plate in the leading edge region, and is
arranged in a single line on the upper surface of the top plate in the
trailing edge region.

6. The turbine blade according to claim 2, whereinthe height of the top
plate is set to be lower than the height of the top surface of the
squealer by at least a predetermined value in consideration of variations
in the finished height of the heat-resistant coating.

7. The turbine blade according to claim 2, whereinthe height of the top
plate of the leading edge region is formed so as to be lower than the
height of the top plate of the trailing edge region, and an inclined
portion which has an upward gradient toward the trailing edge region from
the leading edge region is formed.

8. The turbine blade according to claim 2, whereinthe plurality of cooling
holes is arranged in a double line on the top surface of the squealer or
the upper surface of the top plate in the leading edge region, and is
arranged in a single line on the upper surface of the top plate in the
trailing edge region.

9. The turbine blade according to claim 4, whereinthe plurality of cooling
holes is arranged in a double line on the top surface of the squealer or
the upper surface of the top plate in the leading edge region, and is
arranged in a single line on the upper surface of the top plate in the
trailing edge region.

10. The turbine blade according to claim 7, whereinthe plurality of
cooling holes is arranged in a double line on the top surface of the
squealer or the upper surface of the top plate in the leading edge
region, and is arranged in a single line on the upper surface of the top
plate in the trailing edge region.

Description:

TECHNICAL FIELD

[0001]The present invention relates to a turbine blade having a squealer
at a blade tip thereof.

BACKGROUND ART

[0002]A gas turbine is constituted by a compressor, a combustor, and a
turbine. The air taken in from an air inlet is compressed by the
compressor, and is supplied to the combustor as a high-temperature and,
high-pressure compressed air. In the combustor the compressed air and
fuel are mixed and combusted, and the result is supplied to the turbine
as a high-temperature and high-pressure combustion gas. In the turbine, a
plurality of stator vanes and turbine blades are alternately disposed
within a casing, the turbine blades are rotationally driven by the
combustion gas supplied to an exhaust passage, and the rotational driving
is recovered as electric power by a generator coupled with a rotor. The
combustion gas which has driven the turbine is converted into hydrostatic
pressure by a diffuser, and is emitted to the atmosphere.

[0003]In the gas turbine configured in this way, there is a possibility
that the temperature of the combustion gas which acts on the plurality of
stator vanes and turbine blades reaches 1500° C., and the stator
vanes and the turbine blades are heated and damaged. Therefore, in the
stator vanes and the turbine blades, a cooling flow passage is provided
in an air foil, a blade wall is cooled by a cooling medium, such as
cooling air received from the outside, and when the cooling medium is
made to flow into the combustion gas from cooling holes provided in the
blade wall, the surface of the blade is cooled by film cooling, etc.

[0004]Meanwhile, between a blade tip (apex) of each turbine blade which is
rotationally driven, and a ring segment constituting the portion of the
casing, a predetermined gap is provided so that both the blade tip and
the ring segment do not interfere with each other. However, if the gap is
too large, since a portion of the combustion gas flows over the blade tip
and flows away to the downstream, energy loss occurs, which reduces the
thermal efficiency of the gas turbine. In order to suppress the leak of
the combustion gas from this gap, the blade tip of the turbine blade is
provided with a squealer (also referred to as a thinning) which functions
as damming, and the gap between the top surface of the squealer and the
ring segment is made as small as possible to prevent a decrease in the
thermal efficiency of the gas turbine.

[0005]An example of such a turbine blade is shown in FIGS. 5A and 5B.

[0006]A turbine blade 50 shown in FIG. 5A is erected on a platform 11
embedded in a rotating rotor disc (not shown) via a blade root portion
16, and a rotor (not shown) and the rotor disc (not shown) rotate
integrally. When the section of the turbine blade 50 is seen from the
radial direction of the blade, a pressurized-surface-side blade wall 18
is concavely formed from a leading edge to a trailing edge on the
upstream of the blade in its rotational direction R, and a
suction-surface-side blade wall 19 is convexly formed from the leading
edge to the trailing edge end on the downstream of the blade in its
rotational direction R. A blade tip 15 of the turbine blade 50 is blocked
by a top plate 17. On the top plate 17, a squealer 23 is provided in the
shape of a belt from the leading edge side to the trailing edge side
along the suction-surface-side blade wall 19 in the peripheral direction
of the turbine blade 50, and protrudes radially outward from the blade.
In this configuration, a portion of a combustion gas FG which has come
into contact with the blade surface from the turbine blade 50 on the side
of the pressurized-surface-side blade wall 20 flows along the top plate
17 of the blade tip 15, flows over the squealer 23, and flows to a
downstream exhaust passage.

[0007]As shown in FIG. 5B, in order to cool the top plate 17 and the
squealer 23, the blade tip 15 of the turbine blade 50 is provided with
cooling holes 28a and 28b through which a portion of the cooling medium
CA which flows through the cooling flow passage 26 within the air foil 12
is blown off into the combustion gas. Additionally, although a portion of
the combustion gas FG flows through the gap C between the ring segment 60
and the top surface 23a of the squealer 23, this gap flow causes the
energy loss of the turbine, and causes a decrease in the thermal
efficiency of the gas turbine. Accordingly, it is contrived to make the
gap C as small as possible. Therefore, depending on the operating
conditions of the gas turbine, the top surface 23a of the squealer 23 and
the lower surface of the ring segment 60 rotate while being brought into
contact with each other by the rotation of the turbine blade 50.

[0008]Additionally, in order to protect the blade surface directly exposed
to the high-temperature combustion gas, a heat-resistant coating (also
referred to as TBC) 24 is applied on outside surfaces, such as the top
plate 17 of the blade tip 15, the suction-surface-side blade wall 19, the
pressurized-surface-side blade wall 20, and a side wall 23d of the
squealer, thereby interrupting the heat from the high-temperature
combustion gas in order to prevent the damage of the blade surface. In
this regard, as described above, since the gap C between the top surface
23a of the squealer 23 and the ring segment 60 is adjusted so as to be as
small as possible, it is difficult to apply a heat-resistant coating on
the top surface 23a of the squealer 23, and the base material of an air
foil is exposed to the combustion gas. Therefore, the top surface 23a of
the squealer is protected from the high-temperature combustion gas by the
convection cooling of the cooling medium CA which flows through the
cooling holes 28b.

[0009]Examples of turbine blades in which a squealer is provided at the
whole periphery of a blade wall are disclosed in Patent Documents 1 to 3.

[0013]In recent years, in order to improve the thermal efficiency of a gas
turbine, the temperature of a combustion gas tends to be higher, and the
cooling of a turbine blade needs to be reinforced. Additionally, although
the squealer disposed at the blade tip of the turbine blade described
above is provided on the upper surface of the top plate from the
leading-edge-side to the trailing edge side along the blade wall of the
blade tip, since the width of the blade is narrow at the trailing edge
side there is a possibility that the space in which cooling holes are
provided is limited, and cooling becomes insufficient. Meanwhile, on the
top surface 23a of the squealer, the surface of the base material of the
air foil is exposed to the combustion gas. Thus, when the squealer is
insufficiently cooled at the trailing edge side, there is a problem in
that the squealer is damaged under the influence of the high-temperature
combustion gas.

[0014]The object of the present invention is to provide a turbine blade
having a squealer on tip which solves such a problem.

Means for Solving the Problem

[0015]In order to achieve the above object, a turbine blade of the
invention includes a air foil including a plurality of cooling flow
passages through which a cooling medium flows from a leading edge region
to a trailing edge region, a top plate which forms the apex of the air
foil and has a heat-resistant coating applied on the upper surface
thereof, and which includes a plurality of cooling holes, and a squealer
which protrudes radially outward from the blade from the top plate, and
is formed so as to extend from a leading edge end to a starting end of
the trailing edge region along a suction-surface-side blade wall in a
peripheral direction of the blade.

[0016]In this case, since the squealer is formed from the leading edge end
to the starting end of the trailing edge region along the
suction-surface-side blade wall in the peripheral direction of the blade,
and the squealer is not provided in the trailing edge region which is apt
to be insufficiently cooled, the damage of the squealer is prevented.
Additionally, in the trailing edge region in which the squealer is not
provided, a heat-resistant coating is applied on the upper surface of the
top plate to make the gap between it and the ring segment small, so that
the loss of energy can be reduced and the damage by the combustion gas
can also be prevented.

[0017]Additionally, a turbine blade of the invention includes an air foil
including a plurality of cooling flow passages through which a cooling
medium flows from a leading edge region to a trailing edge region, a top
plate which forms the apex of the air foil and which has a heat-resistant
coating applied on the upper surface thereof, and which includes a
plurality of cooling holes, and a squealer which protrudes radially
outward from the blade from the top plate, which is formed from a
starting end of the trailing edge region along a suction-surface-side
blade wall to a leading edge end in a peripheral direction of the blade,
and is further formed so as to continuously extend from the leading edge
end along a pressurized-surface-side blade wall to the starting end of
the trailing edge region.

[0018]In this case, since the squealer is formed from the starting end of
the trailing edge region along the suction-surface-side blade wall to the
leading edge end in the peripheral direction of the blade, and is further
formed so as to continuously extend from the leading edge end along the
pressurized-surface-side blade wall to the starting end of the trailing
edge region, and the squealer is not provided in the trailing edge region
which is apt to be insufficiently cooled, the damage of the squealer is
prevented. Additionally, in the trailing edge region in which the
squealer is not provided, a heat-resistant coating is applied on the
upper surface of the top plate to make the gap between it and the ring
segment small, a gap flow leaking out of the blade tip becomes smaller,
and the loss of energy is further reduced.

[0019]The height of the top plate may be set to be lower than the height
of the top surface of the squealer by at least a predetermined value in
consideration of variations in the finished height of the heat-resistant
coating.

[0020]In this case, since the top plate is set to be lower than the top
surface of the squealer by a predetermined value, even if the gap between
the ring segment and the blade tip becomes small, the contact between the
top plate and the ring segment can be prevented.

[0021]The height of the top plate of the leading edge region may be formed
so as to be lower than the height of the top plate of the trailing edge
region, and an inclined portion which has an upward gradient toward the
trailing edge region from the leading edge region may be formed.

[0022]In this case, since the height of the top plate of the leading edge
region is formed so as to be lower than the height of the top plate of
the trailing edge region, the heavy contact between the ring segment and
the top plate can be prevented, and the stable operation of the gas
turbine is allowed.

[0023]The plurality of cooling holes may be arranged in a double line on
the top surface of the squealer or the upper surface of the top plate in
the leading edge region, and is arranged in a single line on the upper
surface of the top plate in the trailing edge region.

[0024]In this case, since the double-line cooling holes are arranged in
the top surface of the squealer or the upper surface of the top plate in
the leading edge region, and the single-line cooling holes are arranged
in the upper surface of the top plate in the trailing edge region, the
insufficient cooling of the top plate and the squealer in the leading
edge region and the trailing edge region are compensated for, and the
damage of the top plate and the squealer can be prevented.

Advantage of the Invention

[0025]According to the present invention, since the damage of the squealer
by a high-temperature combustion gas is prevented, and the loss of the
combustion gas which flows over the turbine blade can be suppressed, a
decrease in the thermal efficiency of a gas turbine can be prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026]FIG. 1 shows a perspective view of a turbine blade according to a
first embodiment.

[0027]FIG. 2A shows a schematic plan view of a blade tip of the turbine
blade according to the first embodiment.

[0028]FIG. 2B shows a portion of a cross-section (section A-A of FIG. 2A)
in an erected direction of the turbine blade shown in FIG. 2A.

[0029]FIG. 3A shows a perspective view of a turbine blade according to a
second embodiment.

[0030]FIG. 3B shows a schematic plan view of the turbine blade according
to the second embodiment.

[0031]FIG. 4A shows a perspective view of a turbine blade according to a
third embodiment.

[0032]FIG. 4B shows a portion of a cross-section (section B-B of FIG. 4A)
in an direction of the turbine blade according to the third embodiment.

[0033]FIG. 5A shows a perspective view of a turbine blade of a
conventional technique.

[0034]FIG. 5B shows a schematic sectional view of the turbine blade of the
conventional technique.

BEST MODE FOR CARRYING OUT THE INVENTION

[0035]Hereinafter, preferred embodiments of a turbine blade having a
squealer according to the present invention will be described in detail
with reference to the accompanying drawings. In addition, the present
invention is not limited by these embodiments. Furthermore, constituent
elements of these embodiments include elements which can be easily
replaced by a person skilled in the art, or substantially the same
elements.

[0036]FIG. 1 shows a perspective view of a turbine blade according to a
first embodiment, FIG. 2A shows a schematic plan view of a blade tip of
the turbine blade shown in FIG. 1, and FIG. 2B shows a portion of a
cross-section (section A-A of FIG. 2A) in an erected direction of the
turbine blade shown in FIG. 1. Common to individual constituent elements
of a moving blade described in a conventional technique in terms of names
or symbols will be described using the same names and symbols.

[0037]As shown in FIG. 1, the turbine blade 10 according to the first
embodiment of the present invention is erected on a platform 11 embedded
in a rotor disc (not shown) via a blade root portion 16, and a rotor (not
shown) and the rotor disc rotate integrally. When the air foil 12 of the
turbine blade 10 is seen from the radial direction of the rotor, a
pressurized-surface-side blade wall 18 is concavely formed from a leading
edge end 21 to a trailing edge end 22 on the upstream of the rotor in its
rotational direction R, and a suction-surface-side blade wall 19 is
convexly formed from the leading edge end 21 to the trailing edge end 22
on the downstream of the rotor in its rotational direction R. The width
of the blade becomes smaller toward the trailing edge end 22.
Additionally, in this embodiment, as for the shape of the air foil 12
when being seen from the radial direction of the rotor, a region in the
vicinity of the leading edge end 21 is defined as a leading edge region
13, a region in the vicinity of the trailing edge end 22 is defined as a
trailing edge region 14, and a region between the leading edge region 13
and the trailing edge region 14 is defined as an intermediate region.
Also, the boundary between the trailing edge region 14 and the
intermediate region is defined as a starting end 14a of the trailing edge
region 14.

[0038]The apex of the blade tip 15 of the air foil 12 is blocked by a top
plate 17. A squealer 23, which extends radially outward from the rotor
from the suction-surface-side blade wall 19, and extends from the leading
edge end 21 to the starting end 14a of the trailing edge region 14 along
the suction-surface-side blade wall 19 of the upper surface 17t of the
top plate 17 in a peripheral direction of the air foil 12, is arranged on
an upper surface 17t of the top plate 17. In addition, since the turbine
blade 10 is exposed to a high-temperature combustion gas, similarly to
the turbine blade of the conventional technique shown in FIGS. 5A and 5B,
a cooling flow passage through which a cooling medium flows is provided
inside the air foil 12, the cooling medium is received from the blade
root portion 16, and the air foil is cooled by convection cooling within
the air foil 12, film cooling on the surface of the blade, and the like
(the details thereof will be described later).

[0039]As shown in FIG. 2A, in the blade tip 15 of the air foil 12 of the
turbine blade 10, the squealer 23 is arranged to the starting end 14a of
the trailing edge region 14 along the suction-surface-side blade wall 19
with the leading edge end 21 as a starting point, and the squealer is not
provided to a trailing edge end 22 from the starting end 14a. That is,
the portion of the upper surface 17t of the top plate 17 along the
suction-surface-side blade wall 19 does not provide a squealer between
the starting end 14a of the trailing edge region 14 and the trailing edge
end 22, and is finished to the same height as the top plate 17 of the
trailing edge region 14, and the upper surface 17t of the top plate 17
extends to the edge of the suction-surface-side blade wall 19.
Additionally, the upper surface 17t of the top plate 17 along the
pressurized-surface-side blade wall 20 from the leading edge end 21 to
the trailing edge end 22 is not provided with a squealer.

[0040]FIG. 2B shows a cross-section (section A-A of FIG. 2A) in an erected
direction of the blade shown in FIG. 2A. In order to prevent the damage
by the high-temperature combustion gas, a heat-resistant coating 24 is
applied on the whole upper surface 17t of the top plate 17. As described
above, the squealer 23 arranged on the upper surface 17t of the top plate
17 is formed along the suction-surface-side blade wall 19 from the
leading edge end 21 to the starting end 14a of the trailing edge region
14, and a squealer is not arranged from starting end 14a of the trailing
edge region 14 to the trailing edge end 22. Instead, the upper surface
along the suction-surface-side blade wall 19 from starting end 14a of the
trailing edge region 14 to the trailing edge end 22 is finished so to be
flush with the upper surface 17t of the top plate 17. Additionally, the
heat-resistant coating 24 is applied on the upper surface 17t of the top
plate 17, and the gap between the lower surface of the ring segment 60
and the upper surface 17t of the top plate 17 after the application of
the heat-resistant coating is set to become as small as possible.

[0041]Additionally, it is important to suppress the height of the upper
surface 17t of the top plate 17 after the application of the
heat-resistant coating 24 of the trailing edge region 14 so as to be
lower than a top surface 23a of the squealer 23 by a height difference H.
Such a height difference is based on me following reasons.

[0042]The top surface 23a of the squealer 23 is the surface of a base
material of the air foil 12 on which a heat-resistant coating is not
applied and which is finished by machining. Meanwhile, as for the
heat-resistant coating 24 laminated on the upper surface 17t of the top
plate 17, the finishing precision equivalent to that of a machining
surface is not obtained. That is, since the heat-resistant coating is not
applied by plasma spraying etc., it is difficult to obtain a surface
roughness equivalent to that of a machining surface, and a high-precision
finished surface cannot be formed. Therefore, the upper surface 17t
including the thickness of the heat-resistant coating of the top plate 17
is made lower than the top surface 23a of the squealer 23 by at least a
predetermined value (height difference H) in consideration of the maximum
variation range of the finished height of the heat-resistant coating.
That is, even when the heat-resistant coating is formed with a greatest
thickness, if the height difference between the upper surface 17t of the
heat-resistant coating and the top surface 23a of the squealer 23 is
maintained at a predetermined value (height difference H) or more, the
upper surface 17t of the top plate 17 after the application of the
heat-resistant coating will not become higher than the height of the top
surface 23a of the squealer 23. Accordingly, there is no possibility that
the top plate 17 of the trailing edge region 14 may contact the lower
surface of the ring segment 60 even if the top surface 23a of the
squealer 23 comes into contact with the lower surface of the ring segment
60 according to the operation conditions of a gas turbine. In addition,
it would be better if the predetermined value is at least 0 (zero) mm or
more.

[0043]In addition, applying heat-resistant coating on other blade
surfaces, for example, the suction-surface-side blade wall 19, the
pressurized-surface-side blade wall 20, and the side walls 23d of the
squealer 23 is the same as that of the aforementioned conventional
technique.

[0044]Next, the positional relationship between the squealer 23 and the
cooling flow passage in the air foil 12 will be described with reference
to FIG. 2B. Cooling flow passages 26 and 27 which receive a cooling
medium CA via a cooling flow passage (not shown) bored in the blade root
portion 16 from the rotor disc (not shown) side are arranged within the
air foil 12. The cooling medium CA which cools the air foil 12 of the
trailing edge region 14 is received from a cooling flow passage 26a, and
is discharged into the combustion gas from the trailing edge end 22, and
the cooling medium CA which cools the air foil 12 on the side of the
leading edge is received by the cooling flow passage 27 from the blade
root portion 16 side, and is discharged into the combustion gas from the
leading edge end 21 side.

[0045]The cooling flow passage 26 (26a, 26b, 26c) forms a serpentine bend
flow passage partitioned by a partition wall 29 which is formed within
the air foil 12 and arranged in the radial direction of the blade. That
is, the cooling medium CA is received from the blade root portion 16
side, and flows through the cooling flow passage 26a toward the blade tip
15, and like the arrow of the cooling medium CA shown in FIG. 2B, the
cooling medium flows back at the blade tip 15, and flows through the
cooling flow passage 26b in a downward direction (in a radial inward
direction of the blade) toward the blade bottom 25, During this time, the
cooling flow passage 26a and the cooling flow passage 26b are partitioned
by a partition wall 29b. Moreover, the cooling medium CA flows back at
the blade bottom 25, and flows through a final cooling flow passage 26c
in an upward direction (in a radial outward direction of the blade)
toward the blade tip 15. The space between the cooling flow passage 26b
and the final cooling flow passage 26c is partitioned by a
leading-edge-side partition wall 29c. Additionally, the space between the
cooling flow passage 26a and the cooling flow passage 27 is completely
partitioned by a partition wall 29a.

[0046]The cooling medium CA which flows through the final cooling flow
passage 26c toward the blade tip 15 flows into a trailing edge cooling
portion 30, cools the blade wall 18 on the side of the trailing edge, and
is discharged into a combustion gas from the trailing edge end 22. The
trailing edge cooling portion 30 shown in FIG. 2B adopts a multi-hole
cooling method. A number of cooling holes 31 are bored in the trailing
edge cooling portion 30 so as to pass through the trailing edge cooling
portion 30 from the blade bottom 25 side to the blade tip 15. Each
cooling hole 31 communicates with the final cooling flow passage 26c on
the upstream, and opens into the combustion gas via the trailing edge end
22 on the downstream. While the cooling medium CA flows through the
cooling holes 31, the convection cooling of the blade wall 18 of the
trailing edge cooling portion 30 is performed.

[0047]Additionally, the top plate 17 of the blade tip 15 is also cooled by
the cooling medium CA which flows through the cooling flow passages 26
and 27. However, since the flow velocity of the combustion gas which
flows over the squealer 23 is fast at the squealer 23 arranged on the
upper surface 17t of the top plate 17 so as to protrude therefrom, a
thermal load becomes higher than that of the top plate 17, which results
in insufficient cooling. Therefore, a cooling flow passage 28, of which
one end communicates with the cooling flow passages 26 and 27 and of
which the other end communicates with the cooling holes 28a and 28b
provided in the upper surface 17t of the top plate 17 and the top surface
23a of the squealer 23, is provided. By blowing off the cooling medium
into the combustion gas, the convection cooling of the top plate 17 and
the squealer 23 is performed to prevent these from being insufficiently
cooled. In addition, the cooling holes 28b opened to the top surface 23a
of the squealer 23, as shown in FIG. 5B, may be provided on the side of
the suction-surface-side blade wall 19 in the vicinity of the boundary
between the suction-surface-side blade wall 19 and the top surface 23a
without being opened on the top surface 23a. If the cooling holes are
opened at this position, when the top surface 23a comes into contact with
the lower surface of the ring segment 60, there is no possibility that
the cooling holes 28b are crushed, and a turbine can be stably operated.

[0048]As shown in FIGS. 2A and 2B, the cooling holes 28b provided along
the suction-surface-side blade wall 19 are opened to the top surface 23a
of the squealer 23 via the cooling flow passage 28 from the cooling flow
passages 26 and 27 side, from the leading edge end 21 (squealer end 23b)
to the squealer end 23c, and cooling holes 28c provided along the
suction-surface-side blade wall 19 provided from the end 23c of the
squealer 23 to the trailing edge end 22 are opened to the upper surface
17t of the top plate 17.

[0049]However, the cooling medium CA which flows through the inside of the
air foil 12 exchanges heat with the inner wall of a cooling flow passage,
and is turned into a hot cooling medium in the course of flowing through
the cooling flow passages 26a and 26b and the final cooling flow passage
26c from the leading edge region 13 to the trailing edge region 14, and
flows into the trailing edge cooling portion 30. Although the top plate
17 of the trailing edge region 14 is also cooled by the cooling medium
which Sows through the trailing edge cooling portion 30, since the
temperature of the cooling medium is high, cooling is apt to be
insufficient.

[0050]Moreover, as shown in FIG. 2A, since the width of the blade is
narrow in the trailing edge region 14, double-line cooling holes cannot
be provided unlike the leading edge region 13, but only single-line
cooling holes can be provided. That is, although double-line cooling
holes 28a and 28b line are arranged on both sides of the
suction-surface-side blade wall 19 and the pressurized-surface-side blade
wall 20 of the leading edge region 13 from the leading edge end 21 on the
upper surface 17t of the top plate 17 of the leading edge region 13, only
single-line cooling holes 28c can be arranged from the starting end 14a
of the trailing edge region 14 to the trailing edge end 22. In addition,
the single-line cooling holes 28c of the trailing edge region 14 may be
arranged along the suction-surface-side blade wall 19, may be arranged
along the pressurized-surface-side blade wall 20, and may be arranged
along an intermediate line between the suction-surface-side blade wall 19
and the pressurized-surface-side blade wall 20.

[0051]Since only single-line cooling holes 28c can be arranged in the
trailing edge region 14, the trailing edge region is a region which is
hard to cool as compared with the leading edge region 13, Since the
squealer 23 has a high thermal load, the squealer is a portion which is
especially hard to cool. Here, as for the single-line and double-line
cooling holes, as seen in a cross-section vertical to a centerline
(camber line) of the width of the blade which connects the trailing edge
end 22 from the leading edge end 21 in the plan view of the blade shown
in FIG. 2A, on either the top surface 23a of the squealer or the upper
surface 17t of the top plate 17 from the suction-surface-side blade wall
19 to the pressurized-surface-side blade wall 20, a case where one line
of cooling holes is arranged is referred to as the single-line cooling
holes and a case where two or more lines of cooling holes are arranged is
referred to as the double-line cooling holes.

[0052]In order to avoid the damage of the above squealer, the squealer 23
formed to the trailing edge region 14 along the suction-surface-side
blade wall 19 with the leading edge end 21 as a starting point is cut at
the starting end 14a of the trailing edge region 14 without extending to
the trailing edge end 22. That is, the suction-surface-side end 23c of
the squealer 23 is positioned at the position of the starting end 14a of
the trailing edge region 14. The position of the starting end 14a
coincides with the position of the partition wall 29c on the side of the
leading edge in the plan view in the partition wall which forms the final
cooling flow passage 26c in the air foil 12 (refer to FIG. 2B). That is,
the squealer is not provided from the suction-surface-side end 23c of the
squealer 23 to the trailing edge end 22, and finishing is performed so as
to provide the. same height as the top plate 17 of the trailing edge
region 14.

[0053]Here, the meaning of the starting ends of the trailing edge region
14 and the trailing edge region 14 will be described with reference to
the plan view and sectional view of the turbine blade shown in FIGS. 2A
and 2B. As described above, the trailing edge region 14 is a region which
is insufficiently cooled when compared with the leading edge region 13,
and a place where the damage of the squealer tends to occur from the
constraints of the installation space of the cooling holes, and the
cooling air temperature included in the trailing edge cooling portion 30.
That is, the trailing edge region 14 is a region including the above
trailing edge cooling portion 30, and the final cooling flow passage 26c
on the upstream thereof, and the leading edge region 13 is a region from
the leading edge of the blade to the intermediate region excluding the
trailing edge region 14 in FIG. 2A. The boundary 14a between the
intermediate region and the trailing edge region 14, i.e., the starting
end (position where the trailing edge region 14 starts) of the trailing
edge region 14, coincides with the leading-edge-side partition wall 29c
in the plan view of the partition wall which forms the final cooling flow
passage 26c in the air foil 12. The planar position of the
leading-edge-side partition wall 29c is considered to be the starting end
14a of the trailing edge region 14, and the region from the starting end
14a to the trailing edge end 22 is a region which is apt to be
insufficiently cooled. Although it is desirable that the starting end 14a
of the trailing edge region 14 be closer to the trailing edge end 22, the
position of the starting end changes due to a thermal load applied to the
blade. That is, although the starting end 14a of the trailing edge region
is positioned at the position of the above leading-edge-side partition
wall 29c if the thermal load to the blade is high, it is desirable to set
the starting end to the position of the inlet port wall 30a of the
trailing edge cooling portion 30 if the thermal load is small.
Accordingly, the starting end 14a of the trailing edge region exists
between the leading-edge-side partition wall 29c and the inlet port wall
30a of the trailing edge cooling portion 30, and may be changed within
the region from the leading-edge-side partition wall 29c to an inlet port
wall 30a of the trailing edge cooling portion 30 due to a thermal load
applied to the blade.

[0054]According to the configuration of an invention shown in the first
embodiment, since the squealer 23 is formed from the leading edge end 21
to the starting end 14a of the trailing edge region 14 along the
suction-surface-side blade wall 19 in the peripheral direction of the
blade, the region from the starting end 14a to the trailing edge end 22
is not provided with the squealer and is set to be flush with the top
plate 17, and the heat-resistant coating 24 is not applied on the upper
surface 17t of the top plate 17 where the squealer is not provided, the
damage of the squealer can be prevented. Additionally, since the squealer
23 is provided from the leading edge end 21 to the starting end 14a of
the trailing edge region 14, the gap flow of the combustion gas which
flows over the blade tip 15 of the turbine blade can be made small.

[0055]Additionally, the heat-resistant coating 24 is applied on the upper
surface 17t of the top plate 17 between the starting end 14a of the
trailing edge region 14 in which the squealer 23 is not provided and the
trailing edge end 22, whereby the gap between the lower surface of the
ring segment and the upper surface of the top plate after application of
the heat-resistant coating is set to be as small as possible.

[0056]Moreover, the magnitude of the gap flow which flows over the blade
tip by the combustion gas which flows through an exhaust passage changes
due to the differential pressure between the positive pressure
(pressurized surface) applied to the pressurized-surface-side blade wall
20 and the suction (suction-surface) applied to the suction-surface-side
blade wall 19. Since a differential pressure is markedly smaller in the
trailing edge region than in the leading edge region, the influence which
the gap flow of the trailing edge region has on the thermal efficiency of
a gas turbine is small. Accordingly, according to this embodiments the
damage of the squealer can be prevented, and a decrease in the thermal
efficiency of a gas turbine can also be prevented.

[0057]A second embodiment of a turbine blade according to the present
invention will be described with reference to FIGS. 3A and 3B. FIG. 3A
shows a perspective view of the turbine blade according to the second
embodiment, and FIG. 3B shows a schematic plan view. As shown in FIG. 3A,
the squealer 23 provided on the upper surface 17t of the top plate 17 of
the air foil 12 is formed from the starting end 14a of the trailing edge
region 14 along the suction-surface-side blade wall 19 to the leading
edge end 21, and is formed in a continuous belt shape from the leading
edge end 21 along the pressurized-surface-side blade wall 20 to the
starting end 14a of the trailing edge region 14. That is, both the
pressurized-surface-side end 23b and the suction-surface-side end 23c of
the squealer 23 are formed, at the starting end 14a of the trailing edge
region 14. In addition, the cooling holes 28b, which the cooling medium
CA is blown off from the cooling flow passages 26 and 27 within the air
foil 12, are opened to the top surface 23a of the squealer 23 of this
embodiment. Since other configurations are the same as those of the
above-described second embodiment, the description of these
configurations is omitted.

[0058]According to the second embodiment of the turbine blade related to
the present invention, compared with a first embodiment, the squealer 23
arrives at the leading edge end 21 along the suction-surface-side blade
wall 19 from the starting end 14a of the trailing edge region 14, is
arranged to the starting end 14a of the trailing edge region 14 along the
pressurized-surface-side blade wall 20, and the squealer is not provided
from the starting end 14a of the trailing edge region 14 to the trailing
edge end 22. Therefore, the damage of the squealer can be prevented.
Additionally, since the squealer 23 is provided on both sides of the
suction-surface-side blade wall 19 and the pressurized-surface-side blade
wall 20, the gap flow of the combustion gas which flows over the squealer
and flows into a downstream exhaust passage decreases, and a decrease in
the thermal efficiency of a gas turbine can be further suppressed as
compared with the first embodiment. Other operations and effects are the
same as those of the first embodiment.

[0059]A third embodiment of a turbine blade according to the present
invention will be described with reference to FIGS. 4A and 4B.

[0060]As shown in FIGS. 4A and 4B, the first and second embodiments are
the same in that the top plate 17 is formed by a smooth surface from the
leading edge region 13 to the trailing edge region 14, and the blade tip
15 is blocked. Additionally, the first and second embodiments are the
same in that the squealer 23 is provided along the suction-surface-side
blade wall 19 and the pressurized-surface-side blade wall 20 from the
leading edge region 13 to the trailing edge region 14, and the height of
the upper surface 17t of the top plate 17 is set to be lower than the top
surface 23a of the squealer 23 in order to reliably avoid any
interference with the ring segment 60.

[0061]Meanwhile, a gas turbine may be operated in a state where the gap C
between the lower surface of the ring segment 60 and the top surface 23a
of the squealer 23 becomes small, and both surfaces come into contact
with each other according to operation conditions of the gas turbine.
Even in such a state, it is desirable to allow the operation of the gas
turbine while the top surface 23a of the squealer is cut. However, when
the contact state lasts for a long time, the difference (height
difference H1) in height between the top surface 23a of the squealer and
the upper surface 17t of the top plate 17 is set to be as small as
possible in order to make the gap flow small. Therefore, a heavy, contact
state may occur, where the upper surface 17t of the top plate 17 and the
lower surface of the ring segment 60 come into contact with each other
across their entire surfaces, and which results in an inability to
operate.

[0062]Generally, like the first and second embodiments, the top plate 17
is set to have the same height from the leading edge region 13 to the
trailing edge region 14, and the gap between the lower surface of the
ring segment 60 and the upper surface 17t of the top plate 17 is set to
be constant.

[0063]However, in order to avoid the occurrence of the above situation,
the leading edge region 13 is formed to be lower than the trailing edge
region 14, and the top plate 17 of this embodiment is formed to have a
smooth upward gradient from the leading edge region 13 to the trailing
edge region 14. That is, the leading edge region 13 of the top plate 17
is formed with a planar lower portion 17a, the trailing edge region 14 is
formed with a planar higher portion 17b, and the higher portion 17b is
set to be higher than the lower portion 17a radially outward from the
blade. Additionally, the higher portion 17b of the trailing edge region
14 is set to be lower than the top surface 23a of the squealer 23.
Moreover, the top plate 17 is formed with an inclined portion 17c which
has a smooth upward gradient toward the higher portion 17b from the lower
portion 17a. Additionally, since the surface connected to the higher
portion 17b of the top plate 17 through the inclined portion 17c from the
lower portion 17a of the top plate 17 is formed by a sloped smooth
surface, a gap flow flows over this upper surface is not disturbed.

[0064]The heat-resistant coating 24 is applied on the upper surface 17t of
the whole top plate 17. Although the heat-resistant coating 24 is also
applied on the upper surface of the higher portion 17b of the trailing
edge region 14, the height of the higher portion 17b after the
application of the heat-resistant coating is suppressed so as to be lower
than the height of the top surface 23a of the squealer 23 by the height
difference H1. Additionally, the height of the higher portion 17b alter
the application of the heat-resistant coating is set to be higher than
the height of the lower portion 17a after the application of the
heat-resistant coating of the leading edge region 13 by a height
difference H2.

[0065]Here, the concept of the height difference HI is the same as that of
the first embodiment with respect to variations in the finished height of
heat-resistant coating.

[0066]In addition, the trailing edge cooling portion 30 shown in FIG. 4B
is an example in which a pin fin cooling method is adopted.

[0067]That is, a plurality of cooling holes 31 which supplies the cooling
medium CA to the trailing edge cooling portion 30 arranged in the
trailing edge region 14 is bored in the axial direction of the rotor from
the blade root portion 16 to the blade tip 15 in the trailing-edge-side
partition wall 34 which forms the final flow passage 26c, Additionally,
the trailing edge cooling portion 30 has a region from the
trailing-edge-side partition wall 34 to the trailing edge end 22. In the
meantime, a number of pin fins 32 and a pedestal 33 are arranged from the
blade root portion 16 to the blade tip 15. The trailing edge cooling
portion 30 serves to receive the cooling medium CA from the final flow
passage 26c, and to perform the convection cooling of the blade wall 18
of the trailing edge region 14. The cooling medium CA, which flows
through the final flow passage 26c flows into the trailing edge cooling
portion 30 via the cooling holes 31 bored in the trailing-edge-side
partition wall 34, is convection-cooled at the pin fin 32, and is
discharged into the combustion gas from the trailing edge end 22.

[0068]Even in the trailing edge cooling portion 30 in this embodiment,
similarly to the first and second embodiments, there are constraints
about the installation space of the cooling holes, and the cooling air
temperature included in the trailing edge cooling portion 30.
Accordingly, the configuration in which, in order to solve the problem of
insufficient cooling in the trailing edge region, the squealer 23 is cut
at the starting end 14a of the trailing edge region 14, and the squealer
is not provided from the starting end 14a of the trailing edge region 14
to the trailing edge end 22, is the same as that of other embodiments.

[0069]In this embodiment, although the trailing edge cooling portion 30
has been described by the pin fin cooling method, the multi-hole cooling
method shown in FIG. 2B of the first embodiment may be adopted.
Additionally, the pin fin cooling method may be adopted in the trailing
edge cooling portion 30 of the first embodiment shown in FIG. 23.

[0070]In this embodiment, the reason why the height difference of the top
plate is provided as described above is in order to avoid a situation in
which the ring segment 60 and the top surface 23a of the squealer 23 come
into contact with each other according to the operational conditions of a
gas turbine, the contact state endures, and the heavy contact stats
occurs across the entire surfaces of the ring segment 60 and the upper
surface 17t of the top plate 17. That is, the top surface 23a of the
squealer 23 is the surface of a base material of the air foil 12 on which
a heat-resistant coating is not applied and which is finished by
machining. Meanwhile, as for the upper surface of the heat-resistant
coating 24 laminated on the higher portion 17b of the top plate 17 of the
trailing edge region 14, the finishing precision equivalent to that of a
machining surface is not obtained. Accordingly, the upper surface 17t
including the thickness of the heat-resistant coating of the top plate 17
is made lower than the top surface 23a of the squealer 23 by at least a
predetermined value (height difference H1) in consideration of the
maximum variation range of the finished height of the heat-resistant
coating. Moreover, the upper surface of the higher portion 17b of the top
plate 17 of the trailing edge region 14 is made higher than the upper
surface of the lower portion 17a of the top plate 17 of the leading edge
region 13 by a predetermined value (height difference H2).

[0071]As a result, such a heavy contact state that the lower surface of
the ring segment 60 comes into contact with the entire surface of the
blade tip 15 can be avoided, and the stable operation of a turbine
becomes possible. In addition, applying heat-resistant coating on other
blade surfaces, for example, the suction-surface-side blade wall 19, the
pressurized-surface-side blade wall 20, and the side walls 23d of the
squealer 23, is the same as that applying of heat resistant coating in
the first embodiment and second embodiment.

[0072]In addition, although not shown in FIG. 4B, even in the third
embodiment similarly to FIG. 2B of the first embodiment the cooling flow
passage 28 for the cooling medium which is blown off to the top plate 17
and the squealer 23 from the cooling flow passages 26 and 27 within the
air foil 12 is provided, and the cooling medium is discharged into the
combustion gas from the cooling holes 28a and 28c.

[0073]By providing the configuration of this embodiment, the higher
portion, lower portion, and an inclined portion in which a heat-resistant
coating is applied on the top plate are formed by cutting out the
squealer of the trailing edge region which is apt to be insufficiently
cooled. Thus, the damage of the squealer is prevented and the loss of
energy is reduced. Additionally, since the heavy contact with the top
plate 17 of the blade tip 15 and the ring segment 60 can be avoided, the
stable operation of a gas turbine is allowed.

[0074]In addition, the squealer 23 in the first embodiment is provided
from the starting end 14a of the trailing edge region 14 along the
suction-surface-side blade wall 19 to the leading edge end 21. However,
even a case where the squealer is further extended to the middle of the
leading edge region 13 along the pressurized-surface-side blade wall 20
from the leading edge end 21, that is, the squealer 23 does not reach the
starting end 14a of the trailing edge region 14 along the
pressurized-surface-side blade wall 20 from the leading edge end 21, but
is arranged to the middle of the leading edge region 13, is the same in
basic technical ideas as the first embodiment, and is included within the
scope of the present invention.

[0075]According to the invention, since the damage of the squealer by a
high-temperature combustion gas is prevented, and the loss of the
combustion gas which flows over the turbine blade can be suppressed, a
decrease in the thermal efficiency of a gas turbine can be prevented.

[0076]While preferred embodiments of the invention have been described and
illustrated above, it should be understood that these are exemplary of
the invention and are not to be considered as limiting. Additions,
omissions, substitutions, and other modifications can be made without
departing from the spirit or scope of the present invention. Accordingly,
the invention is not to be considered as being limited by the foregoing
description, and is only limited by the scope of the appended claims.